This problem is of recent origin. Something has changed which is causing the postings to jiggle up and down, making them difficult to read. I even notice it now, looking at the list of postings under “site feedback”. I believe the problem is that the in-line advertisements are updating to new ones, and the new ones have a different vertical size compared to the old ones, making everything below them jump up and down. One solution might be to assign a fixed vertical size for the ads, and those that don’t need that much space, leave the spare space blank.
I have been getting it too for the last couple of days.
I just now watched as the ad changed from Sleeptrain (something like that) to Remanufactured Engines. It appears what happens isn’t that the ads vertical dimension is changing; instead as the ads change for a brief period the vertical size goes to zero.